Biparametric MRI of the prostate

Abstract

Biparametric Magnetic Resonance Imaging (bpMRI) of the prostate combining both morphologic T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) is emerging as an alternative to multiparametric MRI (mpMRI) to detect, to localize and to guide prostatic targeted biopsy in patients with suspicious prostate cancer (PCa). BpMRI overcomes some limitations of mpMRI such as the costs, the time required to perform the study, the use of gadolinium-based contrast agents and the lack of a guidance for management of score 3 lesions equivocal for significant PCa. In our experience the optimal and similar clinical results of the bpMRI in comparison to mpMRI are essentially related to the DWI that we consider the dominant sequence for detection suspicious PCa both in transition and in peripheral zone. In clinical practice, the adoption of bpMRI standardized scoring system, indicating the likelihood to diagnose a clinically significant PCa and establishing the management of each suspicious category (from 1 to 4), could represent the rationale to simplify and to improve the current interpretation of mpMRI based on Prostate Imaging and Reporting Archiving Data System version 2 (PI-RADS v2). In this review article we report and describe the current knowledge about bpMRI in the detection of suspicious PCa and a simplified PI-RADS based on bpMRI for management of each suspicious PCa categories to facilitate the communication between radiologists and urologists.

Keywords: Biparametric magnetic resonance imaging; prostate cancer; prostate imaging reporting and data system.

Figure 1. a–d

Standard layout of prostate image display in a one screen setting. Double clicking in one of the image allows to display this image in full screen mode. On the left side the morphologic axial and sagittal T2W images and on the right side DWI with high b-values (inverted) and ADC map are displayed. Ideally the morphologic T2W and the DW images should be linked at the same table position. With this described display mode, detection and localization of the suspected lesions (hypointense on T2W, hyperintense on DWI with high b-values or hypointense on inverted with corresponding decrease on ADC map), can already be carried out.

Figure 2

The 41 segmentation model proposed for prostate with enlargement of transition zone and presence of median intravescical lobe: fourthy-one sectors/regions: thirty-eight for the prostate, two for the seminal vesicles and one for the external urethral sphincter are identified. In comparison to 39 segmentation model proposed by PI-RADS v2, the 41 segmentation model adds two segments (right and left) of an intravescical median lobe. TZ: transizon zone; CZ: central zone; PZ: peripheral zone; AS: anterior stroma; SV: seminal vesicle; ML: median lobe.

Figure 3. a, b

Lesion score 3 lesions detected in the transizion zone at mild of the prostate on the left side on morphologic axial and coronal T2W images and DWI with high b-values and ADC map. Three-dimensional (3D) reconstruction coronal (a) and oblique (b) is obtained by drawing a freehand region of interest (ROI) around the discernible index lesion on the inverted DWI with high b-value

Figure 4

Simplified PI-RADS (S-PI-RADS) based on biparametric MRI S-PI-RADS category 1: homogeneous intermediate signal intensity (normal) on T2WI and no anormality on DWI/ADC. Follow-up by PSA is indicated. S-PI-RADS category 2: focal rounded, lenticular or irregular mild/moderately or markedly hypointensity area on T2WI without restriction on diffusion on DWI/ADC. Follow-up by PSA and biparametric MRI eventually within 2 years is indicated. S-PI-RADS category 3: includes 1): subgroup a (lesion volume: <0.5 cm3: round lesion moderately hypointense on T2WI (arrow), hyperintense on high b-value DWI (arrow) and inverted(arrow), and moderately hypointense on ADC map (arrow): accurate evaluation of age, clinical informations, periodic monitoring of PSA value and repetition of bpMRI 1 year later is suggested; 2) subgroup b (lesion volume: >0.5 cm3): lenticular lesion moderately hypointense on T2WI (arrow), hyperintense on high b-value DWI (arrow) and inverted (arrow), and moderately hypointense on ADC map (arrow). Targeted biopsy is indicated. S-PI-RADS category 4: includes PI-RADS v2 score 4 (intraglandular lesions) and 5 (lesions extending to an area outside of the prostate or bulging the capsule of the prostate and/or invasion of the seminal vesicles lesions). Focal lenticular lesion markedly hypointense on T2WI (arrow), hyperintense on high b-value DWI (arrow) and inverted (arrow), and markedly hypointense on ADC map (arrow). Targeted biopsy is indicated.